Non-concentric mounting of brake drums is both a performance and safety concern in the heavy vehicle industry. A drum that is mounted in a non-concentric manner overloads a portion of the braking surface during braking events often causing premature failure. In addition, a misaligned (with respect to the hub) drum or wheel can cause vibrations and shimmy. As a result, standard hubs in the heavy vehicle industry typically have pilots that consist of both a wheel mounting feature and drum mounting feature. The diameters of both are controlled by industry specifications put in place to support interchangeability in the marketplace. Common issues in the marketplace include both non-concentric alignment of the brake drum and hub and corrosion welding of the hub and drum in service. Both create a myriad of problems in service.
While all hubs have pilots for drum mounting, none are created in such a way to minimize both non-concentric mounting and corrosion welding of the products in the field. In some locations, external tools are used to ensure proper alignment of the drum to the hub. These are tools that are bolted onto the hub during assembly to aid in the alignment of the drum. Once the wheel and drum is torqued onto the assembly, these tools must be removed. These tools are not part of the system, and still run the risk of non-concentric mounting as they align the drum using the bolt holes (through holes) of the drum. The dimensional tolerance of these holes is not held as tightly as the pilot diameter on the hub. Further, this tool only influences mounting and does not have any influence on corrosion welding of the drum and hub.